Thompson was born and raised in Rochdale, Greater Manchester. Thompson was raised by his mother, having never met his father, who is now deceased. Growing up, Thompson was a talented rugby player, and then worked as a bouncer and a debt collector.[4] He also pursued a career in bodybuilding.[5] Thompson took up the sport of wrestling and competed in a several matches before seeing an MMA match featuring Don Frye (whom he would later fight and beat at Pride 34: Kamikaze), which ultimately inspired him to pursue a career in MMA. He started watching DVDs on boxing, wrestling, and Brazilian jiu-jitsu.

Thompson began his mixed martial arts career fighting in the British promotion Ultimate Combat (UC). He developed a rivalry with Mark "The Shark" Goddard after their bout in Ultimate Combat 6: Battle in the Cage. Thompson won the bout by referee stoppage, but Goddard disputed the result, saying that Thompson had tapped earlier to one of his armbar attempts. A rematch at Ultimate Combat 8: Retribution resulted in an 18 second knockout victory for Thompson. After five straight victories, he faced his first loss to Georgian Tengiz Tedoradze at Ultimate Combat X. Tedoradze managed to stop Thompson's initial charge and won by doctor stoppage after the second round. Thompson bounced back with a UC Championship bout against Ultimate Fighting Championship (UFC) veteran Dan Severn at Ultimate Combat 11: Eyes of the Beast.

Thompson made his EliteXC debut against undefeated 8 - 0 fighter Brett Rogers at the EliteXC: Street Certified on 16 February 2008. Rogers knocked Thompson out in the first round. Despite this loss, Thompson followed up with a headlining appearance at EliteXC: Primetime against streetfighter Kimbo Slice. Entering the fight with a considerably swollen cauliflower ear, Thompson managed to control the first two rounds with effective ground and pound.[6] However, both fighters came into the third round substantially winded. Slice landed several unanswered blows to Thompson's face whilst on his feet, one of which burst his cauliflower ear, prompting the referee to stop the fight and declare a TKO in Slice's favour. The stoppage caused a great deal of controversy.[7]

On 6 February 2009, Thompson fought Steve Bossé at Strike Box/Titans Fighting's inaugural event in Quebec, Canada. The event was originally scheduled to be under Strike Box's own rules where only boxing, takedowns and standing submissions were allowed, but the rules were not accepted by the province's athletic commission in time for the event. It was therefore conducted under MMA rules instead. Before the event some fighters agreed to fight under Strike Box's proposed rules as a gentleman's agreement, though the referee in charge would not have any choice but to allow ground fighting were it to happen. Thompson, who later claimed to be unaware of the agreement, proceeded to take down, mount and ground and pound Bosse - as allowed under MMA rules - after Bosse went for a standing guillotine choke at the start of the fight. This caused the audience to boo Thompson and the referee, unaware of that the fight was being conducted under MMA rules. Beer cans and eventually chairs were then thrown into the ring, prompting referee Yves Lavigne to stop the match. Although it was originally declared a no contest[8][9] the fight and its result doesn't appear on either fighter's official fight records.

Thompson competed in the ZT Fight Night Tournament for £10,000 along with 7 other fighters on 30 January 2010. He avenged his first career loss against Tengiz Tedoradze in the quarterfinals, his first win in nearly three years, breaking a five-loss streak. He was then knocked out by the eventual tournament winner, Rob Broughton.[12]

Rumours that Thompson could face Ikuhisa Minowa at Dream 16 surfaced.[13] However it was later revealed that Minowa would face Satoshi Ishii at Dream 16.[14][15] Thompsony instead fought DEEP veteran Yusuke Kawaguchi and lost via a controversial Split Decision. Many believed the two majority decision judges were biased towards the Japanese home country fighter after Thompson retained top position and did much more damage at the end of the first and throughout the second round.[16]

Thompson fought five-time "World’s Strongest Man" Mariusz Pudzianowski at KSW XVI on 21 May 2011.[17] He won the fight via submission in the second round.

In the rematch at KSW XVII, Thompson lost a controversial decision. After the fight, he launched a profane verbal assault directed at the promotion. Two days later the promotion changed the result to a No Contest, claiming an error in scorecard tallying. Thompson, however, has not participated in any subsequent KSW events.

Thompson fought in the main event of the Super Fight League's inaugural event, SFL 1, against Bob Sapp. He won the fight when Sapp injured his leg as he was being taken down by Thompson, forcing him to tap out to the injury.[18]

He next competed at Super Fight League 3 against Bobby Lashley.[19] The outcome was yet another close and controversial decision, this time going unanimously in Thompson's favor, giving him his first winning streak since 2005.

Thompson returned to action once his orbital bone healed from his previous war with Lashley on 1 March 2014 against UFC veteran Colin Robinson as part of the Underdog Promotions card at the Odyssey Arena, Northern Ireland. He won via arm triangle choke in the second round.

It was announced on 23 May that Thompson had been signed by Bellator Fighting Championship and would make his promotional debut against Eric Prindle in the headlining bout of Bellator 121 on 6 June 2014. Thompson dominated Prindle and won by TKO in the first round at 1:55 minutes.

Thompson was expected to face UFC veteran Houston Alexander in the co-main event on 17 October 2014 at Bellator 129. However on 10 October 2014 it was announced that Thompson was pulled from the fight due to injury.[20]